1. Field of the Invention
The present invention pertains to a medical device for use in therapy of a patient, and more particularly, pertains to a catheter for use in association with laser irradiation.
2. Description of the Prior Art
It is known in the art to use laser energy for medical purposes. A common medical application is in the irradiation of myocardial tissue. For external use, the laser energy may be directly applied. However, when the procedure requires irradiation of tissue which is not readily accessible, the use of a laser catheter is common. A typical application for a laser catheter is in the cardiovascular system. U.S. Pat. Nos. 4,997,431 and 4,985,028, both issued to Isner et al., show laser catheters particularly adapted for laser irradiation of tissue within the cardiovascular system.
The irradiation of tissue must be accomplished with great precision as the danger of also damaging necessary adjacent tissue is always present, especially when the process occurs remotely at the distal end of a relatively long catheter. U.S. Pat. No. 4,785,806 issued to Deckelbaum discusses a system whereby an attempt is made to distinguish different types of tissue using ultra violet fluoroscopy. A similar approach is proposed in U.S. Pat. No. 4,718,417 issued to Kittrell et al. Spectral analysis of reflected light energy is also proposed in U.S. Pat. No. 4,669,467 issued to Willett et al.
However, none of these approaches directly monitor the absorption of the energy by the tissue. It is the production and absorption of laser radiation which produces controlled heating and actually damages the unwanted tissue. The prior art discusses distinguishing the tissue prior to laser irradiation and analyzing the products of the procedure following irradiation, but none of the references measure the absorption activity directly during the laser irradiation process.